The amount of video data needed to depict even a relatively short film can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in image quality are desirable.
For example, video compression may use intra-frame prediction, in which a pixel may be predicted from a reference pixel in the same video frame or slice. When using intra prediction in a lossy mode, transform and quantization operations may occur on a block by block basis, which may limit intra prediction for a given block to the use of reference samples in adjacent blocks for prediction of pixels within the given block. However, Joint Collaborative Team on Video Coding (JCT-VC) within the International Telecommunication Union Telecommunications Standardization Sector (ITU-T), which is responsible for a next generation video coding standard, referred to as High Efficiency Video Coding (HEVC), has considered prediction based on adjacent pixels in a block for lossless coding in intra prediction modes. These prediction techniques may be referred to as pixel-by-pixel, sample-by-sample, or pixel-based intra prediction. However, there are issues with pixel-by-pixel intra prediction for pixels along certain borders of the block being predicted due to the lack of availability of adjacent pixels to be used for the prediction of border pixels along the certain borders.
Further, the entropy encoding for lossless coding for HEVC may have been designed for lossy coding modes. However, the statistics for prediction residuals in lossless coding modes may be much different than the statistics for lossy coding modes. Due to the differing statistics there may be room to improve entropy encoding for lossless coding to take into account the statistics for prediction residuals in lossless coding modes.